tecamp/eich taste knob: **how** does it do what it does?

I believe it's just a tilt EQ. I could be wrong given that it's been close to a decade since I owned my old Puma1000.

 

I agree - it's a tilt EQ. Rotation towards Dry suppresses lows and enhances highs, rotation towards Rich enhances lows and mids and suppresses highs. For me, little Dry helps to enhance the bass articulation and to eliminate hum in acoustically bad spaces, little Rich is great for my single coil fretless bass. It is similar to Tilt function of e.g. Laney Digbeth amps.

 

It's been awhile, but "tilt EQ" is how I recall it -- if there's something more subtle going on, I missed it. (I hear the Timbre control on a Thunderfunk the same way -- I believe Fender made an amp or two with this feature, too.)

For those unfamiliar with the amp, you can hear the effect of the Taste control at 45s and (along with some EQ) at 4:24 and 5:00 of this video.